Magnetic recording medium and magnetic disk apparatus using the same

ABSTRACT

A magnetic recording medium includes an underlayer of a nonmagnetic alloy containing chromium and titanium, a magnetic layer of a Co—Cr—Pt—Ta or Co—Cr—Pt—B alloy, and an intermediate layer of a Co—Cr—Pt alloy and being disposed between the underlayer and the magnetic layer, thereby carrying out high-density information recording and reproducing operation.

This is a continuation application of U.S. Ser. No. 09/444,560, filedNov. 19, 1999, now U.S. Pat. No. 6,623,873.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic recording apparatus used,for example, as an auxiliary storage of a computer and a magneticrecording medium for use with the apparatus, and in particular, to athin-film magnetic recording medium suitable for a magnetic recordingapparatus having a high surface recording density of at least fivegigabits per square inch.

Due to development of the information-oriented society, the quantity ofinformation daily used is rapidly increasing. Consequently, it is highlyrequired to increase the recording density and capacity of magneticrecording apparatus. The magnetic heads employ an inductive head using avoltage change which appears in response to a change of a magnetic fluxwith respect to time. These heads are used for the data recording andreading operations. In contrast the heads of this type, there has beenincreasingly used at a higher speed a composite head including arecording head and a read-back or reproducing head in which theread-back head is a magnetoresistive read-back head having higherefficiency or sensitivity. The magnetoresistive head uses a change inits electric resistance in response to a change in leakage flux from amedium on which data to be read is recorded. Moreover, a giantmagnetoresistive (GMR) head having still higher efficiency orsensitivity has been developed to be put to practice, the GMR head usinga considerably great change in magnetic resistance (giantmagnetoresistive effect or spin valve effect) due to a multilayeredstructure including a plurality of magnetic layers accumulated with anonmagnetic layer therebetween. The giant magnetoresistive effect orspin valve effect is an effect in which relative directions ofmagnetization of the plural magnetic layers arranged with a nonmagneticlayer therebetween are changed by a leakage magnetic field from themedium, which resultantly varies the electric resistance.

The magnetic recording medium practically employed at present includesmagnetic layers made of alloys primarily based on cobalt such asCo—Cr—Pt, Co—Cr—Ta and Co—Cr—Pt—Ta. These cobalt alloys have a hexagonalstructure (hcp structure) in which a c axis is an axis for easymagnetization. Therefore, for an in-plane magnetic recording medium inwhich its magnetization is reversed in a magnetic film plane for therecording of information, the c axis of the cobalt alloys is set to(11.0) orientation for crystallization in which the c axis takes anin-plane direction. However, the (11.0) orientation is unstable andhence it is generally impossible to produce such a cobalt alloy directlyon a substrate. To overcome this difficulty, there has been employed amethod advantageously using a good matching property of a Cr(100) planehaving a body-centered cubic (bcc) structure with the Co(11.0) plane.Namely, an underlayer film of chromium is first formed with (100)orientation on a substrate and then a magnetic layer of a cobalt alloyis epitaxially grown on the underlayer such that the c axis of themagnetic layer of cobalt alloy is oriented (11.0), namely, has anin-plane direction. To further increase the crystal lattice matchingproperty in a boundary between the cobalt alloy magnetic film and thechromium underlayer, there has been adopted a method to add a secondelement to chromium to increase lattice spacing of the chromiumunderlayer. This enhances the (11.0) orientation in the cobalt alloy toresultantly increase coercivity thereof. JP-A-62-257618 andJP-A-63-197018 describe examples of the technology above in whichelements such as vanadium and titanium are added to the chromiumunderlayer. In addition to the increase in coercivity of the recordingmedium, the decrease in noise is an essential factor for a higherrecording density. The magnetoresistive head has quite a highreproducing efficiency and hence is suitable for high-density recording.However, the head is highly efficient not only to reproduced signalsfrom a magnetic recording medium but also highly sensitive to the noise.Therefore, it is required to much more reduce the noise as compared withthe recording medium. Japanese Patent No. 2650282 proposes alloy films,for example, a Cr—Mo film as an underlayer which increases coercivityand coercivity squareness and which decreases the medium noise.JP-A-10-228621 describes a combination of a Cr—Mo underlayer with aCo—Cr—Pt—Ta magnetic film. JP-A-4-221418 describes a magnetic recordingmedium in which a cobalt alloy magnetic layer includes at least platinumand boron to increase coercivity for the increase in the recordingdensity. JP-A-9-293227 describes a combination of a Cr—Mo underlayerwith a Co—Cr—Pt—B magnetic layer.

According to JP-A-10-74314, a Co-based nonmagnetic alloy layer isfabricated below the underlayer to decrease the medium noise. Inaccordance with JP-A-10-143865, chromium and zirconium which arerelatively easily oxidized are added to the Co-based nonmagnetic alloylayer such that a surface of the layer is disposed to atmosphere ofoxygen to be slightly oxidized so as to further decrease the mediumnoise in a stable state. JP-A-9-265619 and JP-A-10-214412 describemagnetic recording medium including a Cr-based underlayer in a b.c.c.structure on an alloy film (seed layer) including zirconium andtitanium.

On the other hand, JP-A-1-303624 describes a magnetic recording mediumhaving a high recording density. The medium includes two magneticlayers, i.e., a first magnetic layer is a Co-based recording film and asecond magnetic layer is a layer which includes cobalt and chromium asprimary elements and to which carbon, titanium, zirconium, niobium, andtungsten are added. However, this medium has a coercivity of 64 kA/m(800 oersted). This is less than the value, 160 kA/m (2000 oersted),required for the present invention. JP-A-5-114128 describes a method tolower the medium noise and to increase the recording density in whichthe medium includes two magnetic films, i.e., a lower layer is aCo—Cr—Ta alloy with a lower medium noise and a higher layer is aCo—Cr—Pt alloy with high coercivity.

It has been commonly known that the medium noise can be effectivelylowered by reducing sizes of crystal grains of the magnetic film andpossibly equalizing grain sizes to each other. The technologies abovealso use this advantageous effect. Such an example is written in pages5351 to 5353 of J. Appl. Phys., vol. 79 (1996). Namely, the crystalgrains become finer by using a Cr—Ti alloy underlayer when compared withthe prior art employing a Cr underlayer, and the matching of the latticeconstant with respect to the Co—Cr—Pt alloy is improved to resultantlyincrease coercivity. It is also known as described in this article thatthe medium noise is efficiently lowered by increasing the Crconcentration of the Co—Cr—Pt magnetic layer. On the other hand,JP-10-143865 describes a medium including a glass substrate. Namely, forexample, when the Cr—Ti alloy underlayer and the Co—Cr—Pt magnetic filmare fabricated after slightly oxidizing a surface of the Co—Cr—Zr seedlayer, the c axis which is an axis for easy magnetization in the h.c.p.structure of the Co—Cr—Pt magnetic layer is oriented to be parallel tothe film surface plane, i.e., in (11.0) orientation, and the crystalgrains becomes finer, leading to a higher signal-to-noise (S/N) ratio.After fabricating a Co—Cr—Zr seed layer with composition of 60 at.%Co-30 at. %Cr-10 at. %Zr, a surface of the seed layer is slightlyoxidized and an 80 at. %Cr-20 at. %Ti underlayer and a Co—Cr—Pt magneticfilm are manufactured thereon to obtain a medium. Having producingsamples of medium with different values of chromium concentration as 73at. %Co-19 at. %Cr-8 at. %Pt, 71 at. %Co-21 at. %Cr-8 at. %Pt, and 69at. %Co-23 at. %Cr-8 at. %Pt, read/write characteristics are evaluatedusing a magnetic recording disk having a surface recording density offive gigabits per square inch. As a result, the read/writecharacteristics are improved as the chromium concentration is increasedin the Co—Cr—Pt magnetic film. For 69 at. %Co-23 at. %Cr-8 at. %Pt, themedium noise takes a minimum value and satisfies the requirementspecified. Reduction in read outputs from these medium containing datawritten in 7090 fr/mm (180 FCI) was examined at about 1000 hours afterthe data write operation. Results show that the read outputs are keptunchanged for the medium of 73 at. %Co-19 at. %Cr-8 at. %Pt and 71 at.%Co-21 at. %Cr-8 at. %Pt. However, the read outputs are reduced about 5%for the medium of 69 at. %Co-23 at. %Cr-8 at. %Pt. If the rate ofreduction in the read outputs is assumed to be fixed with respect tolapse of time, it is expected that the read outputs are lowered about10% in ten years. This is practically a considerable problem for themagnetic recording apparatus. In pages 1528 to 1533 of IEEE Trans. onMagn., vol. 34 (1998), this problem is discussed as a problem of thermalfluctuation in which the intensity of magnetization recorded on a mediumdecreases with a lapse of time. The medium including the 69 at. %Co-23at. %Cr-8 at. %Pt magnetic film has a low S* value of 0.65 and hence alower recording resolution, which does not satisfy the requirementspecified. To examine the problem of thermal fluctuation, theCo—Cr—Pt—Ta magnetic film and the Cr—Mo underlayer described inJP-A-10-228621 are combined with each other to fabricate a sample. Thissample shows a low reduction in the read outputs and a favorablecharacteristic against thermal fluctuation. However, it has been foundthat since the crystal grains become greater for the Cr—Mo underlayer,the medium noise is increased. On a Cr—Ti underlayer which is orientedwith (200) and which has finer crystal grain sizes, a Co—Cr—Pt—Tamagnetic film was fabricated. With a Ta concentration equal to or morethan about 2 at. %, which is effective to withstand thermal fluctuation,the c axis of the magnetic film disperses in a three-dimensional mannerwith respect to the film plane and hence the (11.0) plane cannot beepitaxially grown. Consequently, the magnetic recording medium in whicha Cr—Ti underlayer and a Co—Cr—Pt—Ta magnetic film are accumulated showslow coercivity and low coercivity squareness, and hence there areobtained only insufficient read/write characteristics.

As an example of the medium structure described in JP-A-9-293227,samples of medium including a combination of a Co—Cr—Pt—B magnetic filmand a Cr—Mo underlayer are fabricated. It has been found that the mediumhas a low reduction in the read outputs and a favorable characteristicagainst thermal fluctuation. However, it has been recognized that themedium noise is increased since crystal grains become greater for theCr—Mo underlayer. On a Cr—Ti underlayer which is oriented (200) andwhich has finer crystal grain sizes, a Co—Cr—Pt—B magnetic film wasfabricated. With a boron concentration equal to or more than about 2 at.%, effective to withstand thermal fluctuation, the c axis of themagnetic film in the h.c.p. structure disperses in a three-dimensionalmanner with respect to the substrate plane. Namely, the (11.0) planecannot be epitaxially grown. Therefore, the magnetic recording medium inwhich a Cr—Ti underlayer and a Co—Cr—Pt—B magnetic film are accumulatedshows low coercivity and low coercivity squareness, leading only toinsufficient read/write characteristics.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a magneticrecording medium suitable for implementing a magnetic recordingapparatus with a surface recording density of at least five gigabits persquare inch in which read outputs are only slightly reduced with respectto time even when the medium noise is low, namely, the medium isresistive against thermal fluctuation and has a high recordingresolution, thereby removing the problems above.

The object above can be achieved in accordance with the presentinvention by quasi-epitaxially growing a magnetic layer including aCo—Cr—Pt—Ta or Co—Cr—Pt—B alloy having lower thermal fluctuation on anunderlayer including a Cr—Ti nonmagnetic alloy of which grain sizes canbe reduced. The inventors have found that the condition above can besatisfied by disposing an underlayer including a Cr—Ti-based nonmagneticalloy and an intermediate layer including Co—Cr—Pt. On an underlayer ofCr—Ti alloy in a b.c.c. structure oriented (200) with respect to asubstrate plane, an intermediate layer of a Co—Cr—Pt alloy is fabricatedto thereby produce a Co—Cr—Pt alloy in an h.c.p. structure oriented(11.0). On the intermediate layer, a magnetic layer including aCo—Cr—Pt—Ta or Co—Cr—Pt—B alloy having an h.c.p. structure like theCo—Cr—Pt alloy is grown. Through an epitaxial growth, the c axis, i.e.,an axis for easy magnetization is oriented (11.0) to be parallel to thefilm surface plane. The c axis of the magnetic film having the h.c.p.structure is parallel to the film plane, which enhances magneticanisotropy in the plane and hence increases the coercivity and thecoercivity squareness. This advantageously increases the signal-to-noiseratio and the recording resolution. As a result, there is obtained anin-plane magnetic recording medium which is effective to minimize thecrystal grain size of the Cr—Ti underlayer and which is resistiveagainst thermal fluctuation of the magnetic film including a Co—Cr—Pt—Taalloy. The Cr—Ti underlayer has a Ti concentration from about 10 at. %to about 26 at. %, favorably, from about 14 at. % to about 24 at. % forthe following reason. In this Ti concentration range, the crystal grainsize can be easily reduced. In this connection, a Co—Cr—Pt—Ta alloyincludes cobalt as its primary constituent element and further includesat least chromium, platinum, and titanium. In addition to a Co—Cr—Pt—Taalloy, there may be used a Co—Cr—Pt—Ta alloy to which niobium, boron,and titanium are added, the concentration thereof ranging from about oneat. % to about three at. %. In this constitution, the crystal grainsizes can be reduced and homogenized, leading to a favorable effect.When boron is added, the grain size can be minimized and the coercivitycan be increased, which is quite desirable to increase the recordingdensity. Moreover, a Co—Cr—Pt—B alloy is an alloy including cobalt asits primary element and at least chromium, platinum, and boron.

The intermediate layer including the Co—Cr—Pt alloy is favorably aferromagnetic material. Namely, it is then possible to control suchmagnetic properties as coercivity, coercivity squareness, and residualmagnetism. However, when the chromium content is insufficient in theintermediate layer of Co—Cr—Pt alloy, the medium noise becomes greater.When the chromium content is excessive in the Co—Cr—Pt alloy layer, thecoercivity is lowered. Therefore, the chromium concentration isappropriately set to from about 18 at. % to about 24 at. %. The chromiumcontent is more favorably in a range from about 20 at. % to about 24 at.% because the medium noise is remarkably minimized under this condition.To control the coercivity in a range from about 175 kA/m (2.2kilooersted) to about 287 kA/m (3.5 kilooersted), the platinumconcentration is appropriately ranges from about 8 at. % to about 20 at.%. When the tantalum concentration is about 1.5 at. % or less in theCo—Cr—Pt intermediate layer, the medium noise is advantageouslydecreased. This is remarkable especially when a Co—Cr—Pt—B alloy isemployed as the magnetic film. In this situation, when the tantalumconcentration exceeds 1.5 at. %, the (11.0) orientation of theCo—Cr—Pt—Ta intermediate layer is disturbed, which considerably reducesthe coercivity and the coercivity squareness. Therefore, the tantalumconcentration is favorably equal to or less than 1.5 at. %. For a highsurface recording density of at least ten gigabits per square inch, thechromium concentration in the Co—Cr—Pt intermediate layer is favorablyset to about 28 at. % or more so that the layer becomes a nonmagneticfilm, which is more resistive against thermal demagnetization.

To achieve the object above, it is not necessarily needed to fabricate atwo-layer cobalt alloy film in which a Co—Cr—Pt intermediate layer isfabricated below a magnetic layer of a Co—Cr—Pt—Ta or Co—Cr—Pt—B alloy.Namely, the advantage can be similarly obtained by employing a magneticlayer of a Co—Cr—Pt—Ta or Co—Cr—Pt—B alloy having composition of aCo—Cr—Pt as follows in the proximity of a surface thereof which isbrought into contact with the Cr—Ti underlayer. The composition includesthe tantalum or boron concentration which consecutively increases towarda medium surface along the growing direction thereof. When a magneticfilm of which the tantalum or boron concentration has a gradient in adirection of film thickness is used, since the magnetic film includes areduced number of lattice defects, the crystal grain sizes become morehomogenous. This also improves magnetic continuity of the magnetic filmin the film growing direction and hence the inversion of magnetizationbecomes abrupt in the recording operation, which favorably reduces themedium noise.

When a second underlayer which includes chromium as its primary elementand which includes at least one of molybdenum and tungsten is fabricatedbetween an underlayer of a nonmagnetic alloy containing chromium andtitanium and an intermediate layer of a Co—Cr—Pt alloy, there isobtained high coercivity suitable for a higher recording density. Thisadvantage is remarkable when the platinum concentration of the magneticfilm of the Co—Cr—Pt—Ta or Co—Cr—Pt—B alloy ranges from about 12 at. %to about 20 at. % and the total concentration of molybdenum and tungstenin the second underlayer ranges from about 16 at. % to 50 at. %. Whenthe Co—Cr—Pt intermediate layer is at least about four nanometer (nm)thick, the platinum concentration in the intermediate layer desirablyranges from about 12 at. % to about 20 at. % to increase epitaxy of thesecond underlayer and the magnetic layer via the intermediate layer.

The magnetic film favorably has magnetic properties as follows. Thecoercivity measured with a magnetic field applied in the in-plane regionis at least 200 kA/m (2.5 kilooersted), product Br×t between residualmagnetic flux density Br and film thickness t measured under the samecondition is at least 2.0 T.nm (20 Gauss.micron) and at most 10 T.nm(100 Gauss.micron), there can be obtained favorable read/writecharacteristics in a recording density equal to or more than fivegigabits per square inch. When the coercivity becomes less than 200 kA/m(2.5 kilooersted), the read outputs are lowered in a high recordingdensity exceeding 12000 fr/mm (300 kilo-flux reversals per inch (kFCI)).When product Br×t exceeds 10 T.nm (100 Gauss.micron), the read outputsare lowered in a high recording density exceeding 12000 fr/mm (300kFCI). When product Br×t is less than 2.0 T.nm (20 Gauss.micron), theread outputs are minimized in a low recording density. When thecoercivity measured with a magnetic field applied in the in-plane regionis at least 280 kA/m (3.5 kilooersted) and product Br×t measured underthe same condition is at least 2.0 T.nm (20 Gauss.micron) and at most6.5 T.nm (65 Gauss.micron), there are favorably obtained satisfactoryread/write characteristics in a recording density equal to or more than20 gigabits per inch. When the coercivity becomes less than 280 kA/m(3.5 kilooersted), the read outputs are lowered in a high recordingdensity exceeding 16000 fr/mm (400 kFCI). When Br×t exceeds 6.5 T.nm (65Gauss.micron), the read outputs are decreased in a high recordingdensity exceeding 16000 fr/mm (400 kFCI). When Br×t is less than 2.0T.nm (20 Gauss.micron), the read outputs are disadvantageously loweredin a low recording density.

When a film of a material including carbon as its primary element isfabricated with a width ranging from about 3 nm to about 12 nm on themagnetic layer and a lubricant layer of an adsorptive material such asperfluoroalkyl-polyether is disposed on the film with a thickness ofabout 1 nm to about 3 nm, there is obtained a reliable magneticrecording medium applicable to a high density recording operation. Byusing a substrate of an aluminum alloy plated with Ni—P, there can alsobe produced a medium having a reduced medium noise and being moreresistive against thermal fluctuation.

In a magnetic recording disk apparatus including the magnetic recordingmedium above, a driving section to drive the medium in a recordingdirection, a magnetic head including a recording section and a read-backsection, means for relatively moving the head relative to the medium,and read/write signal processing means for inputting a signal to thehead and for reproducing a signal from the head, when the read-backsection of the magnetic head includes a plurality of conductive magneticlayers of which resistance remarkably changes when a direction ofmagnetization of each conductive magnetic layer is relatively changeddue to an external magnetic field and a magnetoresistive sensor disposedbetween the conductive magnetic layers, the sensor including aconductive nonmagnetic layer, i.e., the head being configured in aso-called giant magnetoresistive (GMR) head, there can be obtained asignal intensity for a high recording density and hence a reliablemagnetic recording disk apparatus having a recording density of at leastfive gigabits per square inch.

When the magnetic recording medium of the present invention is used in amagnetic recording disk apparatus, it is desirable that themagnetoresistive head includes a magnetoresistive sensor sectionfabricated between two shield layers which are made of a soft magneticsubstance and which are apart from each other about 0.12 micrometers toabout 0.2 micrometers. When the gap between the shield layers exceeds0.2 micrometers, the read output becomes insufficient in a maximumlinear recording density exceeding 8700 fr/mm (220 kFCI). When the gapis less than 0.12 micrometers, it is difficult to appropriately retaininsulation between the magnetoresistive sensor and each of the shieldlayers.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram showing an example of a cross-sectionalconfiguration of a magnetic recording medium in accordance with thepresent invention;

FIG. 2 is a diagram schematically showing a film fabricating apparatusfor the magnetic recording medium in accordance with the presentinvention;

FIG. 3 is a graph showing a relationship between a residual magneticflux density (Br) and a chromium concentration in a magnetic film of themagnetic recording medium in accordance with the present invention;

FIG. 4 is a graph showing X-ray diffraction patterns of an embodimentand a comparison example of a magnetic recording medium in accordancewith the present invention;

FIG. 5 is a graph showing X-ray diffraction patterns of a medium of thecomparison example of a magnetic recording medium in accordance with thepresent invention;

FIG. 6 is a schematic diagram showing an example of a cross-sectionalconfiguration of a magnetic recording medium in accordance with thepresent invention;

FIG. 7 is a diagram schematically showing a film fabricating apparatusfor the magnetic recording medium in accordance with the presentinvention;

FIG. 8 is a schematic diagram showing an example of a magnetic recordingdisk apparatus in accordance with the present invention; and

FIG. 9 is a diagram schematically showing an example of across-sectional configuration of a magnetic recording medium inaccordance with the present invention.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

FIG. 1 shows a film configuration of a magnetic recording medium of thefirst embodiment. This configuration includes a substrate 10 made of ischemically tempered soda-lime glass of 2.5 inch type. On substrate 10washed, a plurality of layers are fabricated with a tact of nine secondsby a sputtering apparatus (MDP250B) of Intevac. FIG. 2 shows a chamberor station configuration of the sputtering apparatus. On substrate 10,there are fabricated 27 nm thick seed films 11 and 11′ with a 70 at.%Ni-20 at. %Cr-10 at. %Zr alloy, 28 nm thick underlayers 12 and 12′ witha 80 at. %Cr-20 at. %Ti alloy, magnetic intermediate layers 13 and 13′with a 68 at. %Co-22 at. %Cr-10 at. %Pt alloy, magnetic layers 14 and14′ with a 68 at. %Co-21 at. %Cr-8 at. %Pt-3 at. %Ta alloy, and 10 nmthick protective carbon layers 15 and 15′. In each film fabrication, anargon gas is at a pressure of 0.9 Pa (7 mTorr). An oxygen partialpressure monitored by a main chamber 29 during the film fabrication isfrom about 1×10⁻⁷ Pa to about 1×10⁻⁶ Pa (1×10⁻⁹ Torr to about 1×10⁻⁸Torr). The seed layers are manufactured in a seed film chamber 22without heating the substrate and are then heated up to 270° C. by alamp heater in a heating chamber 23. The sheet layers are thereafterexposed to an atmosphere of a mixed gas of 99 vol %Ar-1 vol %O₂ at 0.9Pa (7 mTorr) at a gas flow rate of 20 standard cubic centimeter perminute (sccm) for 3.5 seconds in an oxidization chamber 24. Thereafter,the respective films are fabricated thereon in an underlayer chamber 25,a magnetic intermediate film chamber 26, a magnetic film chamber 27, andprotective film chambers 28 and 28′. After the protective carbon layersare manufactured, a lubricant containing perfluoroalkyl-polyether as itsprimary element is coated thereon to form 1.7 nm thick lubricant films16 and 16′.

As can be seen from Table 1, samples a to c are prepared such that themagnetic intermediate layers and the magnetic layers have thicknesses toset product Br×t of residual magnetic flux density Br of the medium andthickness t of the magnetic film to 7.5 T.nm (75 Gauss.micron).Observation of cross sections of these medium by a transmission electronmicroscope (TEM) shows no clear boundary between the magnetic film andthe intermediate magnetic film, namely, these films are manufactured assubstantially one layer.

Comparison Example 1

The first comparison example is manufactured in the same layerconfiguration and under the same condition as for first embodiment onlyexcepting that magnetic layers 14 and 14′ of the 68 at. %Co-21 at. %Cr-8at. %Pt-3 at. %Ta alloy are not formed; moreover, since product Br×t isassociated with the read output, the thickness of magnetic intermediatelayers 13 and 13′ of 68 at. %Co-22 at. %Cr-10 at. %Pt alloy is set to 21nm for the matching of the read output. FIG. 3 shows in a graph arelationship between the Br value and the chromium concentration inmagnetic recording medium respectively having different chromiumconcentration values in the Co—Cr—Pt magnetic layer, the medium having asquareness S (a ratio of the residual magnetic flux density Br to thesaturation magnetic flux density Bs) equal to about 0.75.

Comparison Example 2

The second comparison example is manufactured in the same layerconfiguration and under the same condition as for first embodiment onlyexcepting that magnetic intermediate layers 13 and 13′ of 68 at. %Co-22at. %Cr-10 at. %Pt alloy are not formed; moreover, since product Br×t isassociated with the read output, the thickness of magnetic layers 14 and14′ of 68 at. %Co-21 at. %Cr-8 at. %Pt-3 at. %Ta alloy is set to 24 nmto obtain Br×t=7.5 T.nm (75 Gauss.micron). The thickness of magneticlayers 14 and 14′ is as shown in FIG. 3. Like chromium, titanium is alsoa nonmagnetic substance, and hence a total concentration of chromium andtitanium of 24 at. % is assumed to be the concentration of chromium toresultantly estimate the value of Br to be 0.31 T (3.1 kilogauss).

Comparison Example 3

The third comparison example is manufactured in the same layerconfiguration and under the same condition as for first embodiment onlyexcepting that a 25 nm thick underlayer of 70 at. %Cr-30 at. %Mo ismanufactured in place of each of magnetic intermediate layers 13 and 13′of 68 at. %Co-22 at. %Cr-10 at. %Pt alloy, magnetic intermediate layers13 and 13′ are not fabricated, and the thickness of magnetic layers 14and 14′ of the 68 at. % Co-21 at. %Cr-8 at. %Pt-3 at. %Ta alloy is setto 24 nm.

TABLE 1 Thickness of Thickness of 68at%Co- 68at%Co-21at%Cr-22at%Cr-10at%Pt 8at%Pt-3at%Ta intermediate Br × t Hc S1f/N Resolutionmagnetic layer (nm) magnetic layer (nm) (T · nm) (kA/m) S* (dB) (%)Embodiment 1a 17 7 7.6 209 0.74 27.5 49.5 Embodiment 1b 11.5 11.5 7.5224 0.77 27.4 50.2 Embodiment 1c 7 15 7.3 244 0.75 27.2 51.5 ComparativeNone 21 7.5 265 0.79 26.1 53.2 Example 1 Comparative 24 None 3.1 1030.20 — — Example 2

TABLE 2 Thickness of 68at%Co-21at%Cr- Thickness of 8at%Pt-3at%Ta70at%Cr-30at%Mo Br × t Hc S1f/N Resolution magnetic layer (nm) secondunderlayer (nm) (T · nm) (kA/m) S* (dB) (%) Comparative 24 25 4.4 1920.61 23.4 47.6 Example 3

Table 1 shows magnetic properties and read/write characteristics of themedium of the first embodiment and the first comparison example andTable 2 shows those of the second and third comparison examples. Themagnetic properties, i.e., coercivity (Hc), coercivity squareness (S*),and product Br×t between total thickness of the magnetic layers andintermediate magnetic layers t and residual magnetic flux density Br aremeasured by applying a maximum magnetic field intensity of 400 kA/m (5kilooersted) at a room temperature by a vibrating sample magnetometer.The read/write characteristics are measured using a magnetic headincluding a read-back element of a spin-valve type having a shield gaplength Gs of 0.18 micrometer and an inductive write element having a gaplength of 0.3 micrometer. S if indicates a soliton read output, N is amedium noise at a linear recording density of 14200 fr/mm (360 kFCI),and a ratio therebetween S lf/N is used to evaluate the medium.“Resolution” indicating the recording resolution is a ratio of the readoutput at 14200 fr/mm (360 kFCI) to the read output at 7090 fr/mm (180kFCI). The medium has a higher recording density as the S lf/N andResolution becomes greater. As can be seen from Table 1, the coercivity(Hc) of medium a, b, and c of the first embodiment can be adjusted byratios of thickness of the Co—Cr—Pt—Ta magnetic layer and the Co—Cr—Ptintermediate magnetic layer. There exists a tendency that S lf/Nincreases and Resolution decreases when the ratio of Co—Cr—Pt—Tamagnetic layer becomes larger than that of Co—Cr—Pt intermediatemagnetic layer. Medium a to c of the first embodiment shows highervalues of S lf/N and Resolution when compared with the second and thirdcomparison examples. The medium of the first comparison example has thehighest value of Resolution, but a lower value of S lf/N. Therefore,each medium of the first embodiment is higher in the error rate about0.5 dB than the first comparison example.

FIG. 4 shows X-ray diffraction patterns respectively of the medium ofthe first embodiment and the first comparison example. For each medium,this graph clearly shows orientation primarily of a (200) plane of theb.c.c. structure of CrTi and orientation of a (11.0) plane of the h.c.p.structure of Co—Cr—Pt—Ta and/or Co—Cr—Pt. In the medium of the secondcomparison example, as shown in the X-ray diffraction patterns in FIG.5, the peak of the (11.0) plane of the b.c.c. structure of Co—Cr—Pt—Tais rarely found. However, since a (00.2) peak is strong, the verticalanisotropy of the magnetic film is increased. Namely, the magnetic filmis vertically magnetized. Therefore, the values of S* and read/writecharacteristics cannot be easily measured in this situation and henceare not shown. In the medium of the third comparison example, althoughthe (11.0) peak of the h.c.p. structure slightly appears, the (00.2)peak of the h.c.p. structure of the Co—Cr—Pt—Ta magnetic layer isstrong. Therefore, the values of Br×t, S*, and Hc are small and henceonly insufficient read/write characteristics are attained.

Embodiment 2

As embodiment 2, a magnetic recording medium is produced in the layerconfiguration of the first embodiment. The medium includes a substrate10 of a chemically tempered alumino-silicate of 2.5 inch type. Substrate10 is first washed and a plurality of layers are fabricated thereon witha tact of eight seconds by a sputtering apparatus (MDP250B) of Intevac.On substrate 10, there are fabricated 25 nm thick seed films 11 and 11′with a 60 at. %Co-30 at. %Cr-10 at. %Zr alloy, 25 nm thick underlayers12 and 12′ with an 78 at. %Cr-22 at. %Ti alloy, 9 nm thick magneticintermediate layers 13 and 13′ with a 67 at. %Co-21 at. %Cr-12 at. %Ptalloy, 9 nm thick magnetic layers 14 and 14′ with a 70 at. %Co-19 at.%Cr-8 at. %Pt-3 at. %Ta alloy, and 8 nm thick protective carbon layers15 and 15′. In each film fabrication, an argon gas is at 0.87 Pa (6.5mTorr). An oxygen partial pressure monitored by main chamber 29 duringthe film fabrication is from about 1×10⁻⁷ Pa to about 7×10⁻⁷ Pa (fromabout 8×10⁻¹⁰ Torr to about 5×10⁻⁹ Torr). The seed layers aremanufactured in seed film chamber 22 without heating the substrate andare then heated up to 270□ by a lamp heater in heating chamber 23. Theseed layers are thereafter exposed to an atmosphere of a mixed gas of 95vol %Ar-4 vol %N₂-1 vol %O₂ at 0.9 Pa (7 mTorr) at a gas flow rate of 21sccm for 3.5 seconds in oxidization chamber 24. Thereafter, therespective films are fabricated thereon in underlayer chamber 25,magnetic intermediate film chamber 26, magnetic film chamber 27, andprotective film chambers 28 and 28′. After the protective carbon layersare manufactured, a lubricant containing perfluoroalkyl-polyether as itsprimary element is applied thereon to form 1.8 nm thick lubricant films16 and 16′.

TABLE 3 Thickness of Thickness of 67at%Co- 70at%Co-19at%Cr-21at%Cr-12at%Pt 8at%Pt-3at%Ta intermediate Br × t Hc S1f/N Resolutionmagnetic layer (nm) magnetic layer (nm) (T · nm) (kA/m) S* (dB) (%)Embodiment 2 9 9 7.2 255 0.78 27.8 54.1

As a result, the magnetic films and the intermediate magnetic filmsbecome smaller in thickness than those of the first embodiment, and thevalue of Hc is increased. As shown in FIG. 3, the read/writecharacteristics of the second embodiment are equal to or more than thoseof the first embodiment.

The medium of the embodiments and the medium of comparison examplesabove are associated with a magnetic recording disk apparatus ofload/unload type and each medium has a flat recording surface. On theother hand, in a magnetic recording disk apparatus of CSS type, tominimize a force of adhesion between a slider on which a magnetic headis mounted and a recording surface of the magnetic recording medium,depressions and projections are required in the surface of the medium.Also in the load/unload type disk apparatus, fine depressions andprojections are required on the surface of the magnetic recording mediumto mitigate impulsive force at a possible occasion of contact betweenthe slider and the medium surface due to an external disturbance such asdust. A magnetic recording medium to satisfy these requirements isfabricated as a third embodiment.

Embodiment 3

FIG. 1 shows a cross-sectional view of embodiment 3 of a magneticrecording medium in accordance with the present invention. The mediumincludes a substrate 60 which is a soda-lime glass of 2.5 inch type witha thickness of 0.635 mm, the glass having a surface chemically tempered.Substrate 60 is first washed and then a plurality of layers arefabricated thereon with a tact of nine seconds by a sputtering apparatus(MDP250B) of Intevac. The sputtering apparatus includes chambers orstations as shown in FIG. 7. On substrate 60, there are fabricated 27 nmthick pre-coat layers 61 and 61′ of a 60 at. %Co-30 at. %Cr-10 at. %Zralloy in a pre-coat chamber 71. The substrate is then heated up to about160 □ by a lamp heater in a first heating chamber 72 to fabricatethereof uneven layers 62 and 62′ including discrete depressions andprojections with a 90 at. %Al-10 at. %Cr alloy in a seed chamber 73 andthen 20 nm thick seed layers 63 and 63′ with a 70 at. %Ni-20 at. %Cr-10at. %Zr alloy in seed chamber 73. The substrate is then heated up toabout 270 □ by a lamp heater in a second heating chamber 74 to beexposed to an atmosphere of a mixed gas of 99 vol %Ar-1 vol %O₂ at apressure of 0.9 Pa (7 mTorr) and at a gas flow rate of 21 sccm for 3.5seconds in an oxidization chamber 77. Thereafter, 30 nm thickunderlayers 64 and 64′ are fabricated thereon with an 80 at. %Cr-20 at.%Ti alloy in an underlayer chamber 78. Fabricated thereon are 11 nmthick magnetic intermediate layers 65 and 65′ with a 68 at. %Co-22 at.%Cr-10 at. %Pt alloy, 11 nm thick magnetic layers 66 and 66′ with a 68at. %Co-21 at. %Cr-8 at. %Pt-3 at. %Ta alloy in a magnetic layer chamber80, and a ten nm thick protective layer 67 and a ten nm thick protectivelayer 67′ in protective layer chambers 81 and 81′ (specifically, a 5 nmthick layer is fabricated in each of chambers 81 ad 81′). Thereafter,the substrate is removed from the sputtering apparatus in a removalchamber 82, and then a lubricant containing perfluoroalkyl-polyether asits primary element is applied thereon to form 1.8 nm thick lubricantfilms 68 and 68′. In the film fabrication of pre-coat layers 61 and 61′,seed layers 63 and 63′, underlayers 64 and 64′, intermediate layers 65and 65′, and magnetic layers 66 and 66′, an argon gas is used as adischarge gas at 0.9 Pa (7 mTorr). In the fabrication of protectivelayers 67 and 67′, an argon gas is used as a discharge gas at 1.3 Pa (10mTorr). To fabricate uneven films 62 and 62′, a mixed gas of 99 vol%Ar-1 vol %O₂ is used at a pressure of 0.9 Pa (7 mTorr). The contour ofthe surface of the medium thus produced is examined by an atomic forcemicroscope. It has been confirmed that about 8 nm high projections arefabricated with a density of about 500 per 10 square micrometer. Theprojection has a diameter of about 100 nm on average. In the evaluationof the medium, the surface is scanned at a speed of about tenmicrometers per second to obtain data at 512 points and the scanningline is shifted with a pitch of 20 nm in a direction vertical to thescanning direction to thereby evaluate the surface contour of an area of10 micrometer×10 micrometer. According to data measured, the surfacecontour has an average roughness factor Ra of from 1 nm to 2 nm. Theheight of projection is defined as that in a range of the bearing curveload ratio from 1% to 99%. Magnetic properties of the medium aremeasured by the vibrating sample magnetometer. Resultantly, coercivityis 221 kA/m (2.78 kilooersted), coercivity squareness is 0.78, Br×tbetween magnetic film thickness t and residual magnetic flux density Bris 7.2 T.nm (72 Gauss.micron), which are equivalent to those of thefirst embodiment.

FIG. 8 shows a magnetic recording disk apparatus including a magneticrecording medium 91 of the second embodiment, a driving section 92 todrive the medium, a magnetic head 93 including a recording section andread-out section, means 94 to move the head 93 relative to the medium91, and read/write signal processing means 95 for inputting a signal tothe head 93 and for reproducing a signal from the head 93. The read-backsection of the magnetic head includes a plurality of conductive magneticlayers of which resistance considerably changes when a direction ofmagnetization of each conductive magnetic layer is relatively changeddue to an external magnetic field and further a magnetoresistive sensordisposed between the conductive magnetic layers, the sensor including aconductive nonmagnetic layer. Namely, the head is configured in aso-called giant magnetoresistive (GMR) head. Read/write characteristicsof the medium are evaluated under the conditions of a 40 nm magneticspacing between the head 93 and the magnetic surface, a linear recordingdensity of 310 kilobits per inch (kBPI), and a track density of 19.5kilo-tracks per inch (KTPI). As a result, the medium of the first tothird embodiments sufficiently satisfies the specifications ofread/write characteristics for a magnetic reading disk apparatus with asurface recording density of six gigabits per square inch. In accordancewith the present invention, the substrate and the glass substrate arenot particularly restricted. Namely, the advantages above can beattained by any known substrates for magnetic recording medium such asan aluminum alloy substrate plated by a Ni—P alloy, glass ceramics, anda silicon substrate.

Next, description will be given of an embodiment in which theintermediate layers of FIGS. 1 and 2 are fabricated with a nonmagneticsubstance.

Embodiment 4

A magnetic recording medium is fabricated as embodiment 4 in the samelayer configuration and under the same condition as for first embodimentonly excepting that each of intermediate layers 13 and 13′ is replacedwith a 7 nm thick 58 at. %Co-30 at. %Cr-12 at. %Pt alloy layer and eachof magnetic layers 14 and 14′ is replaced with a 19 nm thick (64 at.%Co-21 at. %Cr-12 at. %Pt-3 at. %Ta alloy layer. Read/writecharacteristics of the medium are evaluated by the vibrating samplemagnetometer. Resultantly, coercivity is 263 kA/m (3.3 kilooersted),coercivity squareness is 0.76, Br×t is 5.9 T.nm (59 Gauss.micron).Namely, high coercivity is obtained with low Br×t. Moreover, a magneticrecording medium is fabricated in the same layer configuration and underthe same condition as for a fifth embodiment only excepting that 30 nmthick intermediate layers 13 and 13′ are manufactured with 58 at. %Co-30at. %Cr-12 at. %Pt alloy and magnetic layers 14 and 14′ are notfabricated. Read/write characteristics of the medium are evaluated by avibrating sample magnetometer (BHV-50 of Riken-Denshi). Resultantly, themagnetization measuring range is 0.0025 emu and the value of Br×t is toosmall for the measurement, and the intermediate layers 13 and 13′ of 58at. %Co-30 at. %Cr-12 at. %Pt becomes substantially nonmagnetic. Themedium of the fourth embodiment has read/write characteristicssatisfying the specifications of a magnetic recording disk apparatuswith a surface recording density of ten gigabits per square inch. Evenafter the medium is allowed to stand at 70□ for 100 hours, the bit errorrate is deteriorated at most only by 0.5 order of magnitude. When thesurface recording density is ten gigabits per square inch or more, it iseffective to fabricate substantially nonmagnetic intermediate Co—Cr—Ptlayers as in the fourth embodiment. The intermediate layers favorablyhave composition including a chromium concentration of from 28 at. % to40 at. % and a platinum concentration of from 8 at. % to 20 at. %.Thanks to the constitution, the intermediate layers favorably becomesubstantially nonmagnetic and the C—Cr—Pt—Ta layers desirably growepitaxially.

After having actually installing the recording medium above in amagnetic recording disk apparatus, read/write characteristics of themedium are evaluated using a giant magnetoresistive (GMR) head under theconditions of a 40 nm magnetic spacing between the head and the magneticfilm surface, a linear recording density of 310 kBPI (bit per inch), anda track density of 19.5 KTPI (track per inch). As a result, the mediumof the first to third embodiments sufficiently satisfies thespecifications of read/write characteristics for a magnetic reading disksystem with a surface recording density of six gigabits per square inch.In accordance with the present invention, the substrate and the glasssubstrate are not particularly restricted. Namely, the advantages abovecan be attained by any known substrates for magnetic recording mediumsuch as an aluminum alloy substrate plated by a Ni—P alloy, glassceramics, and a silicon substrate.

Embodiment 5

As embodiment 5, a magnetic recording medium is produced in the layerconfiguration as shown in FIG. 1. The medium includes a substrate 10 ofa chemically tempered alumino-silicate of 2.5 inch type. Substrate 10 isfirst washed and a plurality of layers are fabricated thereon with atact of 8.5 seconds by a sputtering apparatus (MDP250B) of Intevac. Thesputtering apparatus includes chambers or stations as shown in FIG. 2.On substrate 10, there are fabricated 40 nm thick seed films 11 and 11′with a 65 at. %Co-20 at. %Cr-15 at. %Zr alloy, 25 nm thick underlayers12 and 12′ with an 80 at. %Cr-20 at. %Ti alloy, magnetic intermediatelayers 13 and 13′ with a 66 at. %Co-22 at. %Cr-12 at. %Pt alloy,magnetic layers 14 and 14′ with a 63 at. %Co-21 at. %Cr-12 at. %Pt-4 at.%B alloy, and 5 nm thick protective carbon layers 15 and 15′. In eachfilm fabrication, an argon gas has a pressure of 0.9 Pa (7 mTorr). Anoxygen partial pressure monitored by main chamber 29 during the filmfabrication is from about 1×10⁻⁷ Pa to about 1×10⁻⁶ Pa (from about1×10⁻⁹ Torr to about 1×10⁻⁸ Torr). The seed layers are manufactured inseed film chamber 22 without heating the substrate and are then heatedup to 220□ by a lamp heater in heating chamber 23. The seed layers arethereafter exposed to an atmosphere of a mixed gas of 99 vol %Ar-1 vol%O₂ at 0.9 Pa (7 mTorr) at a gas flow rate of 20 sccm for 3.5 seconds inoxidization chamber 24. Thereafter, the respective films are fabricatedthereon in underlayer chamber 25, magnetic intermediate film chamber 26,magnetic film chamber 27, and protective film chambers 28 and 28′. Afterthe protective carbon layers are manufactured, a lubricant containingperfluoroalkyl-polyether as its primary element is applied thereon toform 1.5 nm thick lubricant films 16 and 16′. Samples a to c areproduced by setting thicknesses of the intermediate magnetic layers andthe magnetic layers to appropriate values such that product Br×t betweenresidual magnetic flux density of the medium Br and magnetic filmthickness t is about 5 to 6 T.m (50 to 60 Gauss.micron) as shown inTable 4.

Comparison Example 4

Comparison example 4 is manufactured in the same layer configuration andunder the same condition as for the fifth embodiment only excepting thatmagnetic layers 14 and 14′ of 63 at. %Co-21 at. %Cr-12 at. %Pt-4 at. %Balloy are not formed and the thickness of magnetic intermediate layers13 and 13′ of 66 at. %Co-22 at. %Cr-12 at. %Pt is set to 18 nm to obtainproduct Br×t=5 T.nm (50 Gauss.micron) because product Br×t is related tothe read output.

Comparison Example 5

Comparison example 5 is manufactured in the same layer configuration andunder the same condition as for the fifth embodiment only excepting thatmagnetic intermediate layers 13 and 13′ of 66 at. %Co-22 at. %Cr-12 at.%Pt are not formed and the thickness of magnetic layers 14 and 14′ of 63at.%Co-21 at. %Cr-12 at. %Pt-4 at. %B alloy is set to 21 nm.

Comparison Example 6

Comparison example 6 is manufactured in the same layer configuration andunder the same condition as for the fifth embodiment only excepting that25 nm thick underlayers of an 80 at. %Cr-20 at. %Mo alloy are fabricatedin place of intermediate magnetic layers 13 and 13′, magneticintermediate layers 13 and 13′ of 66 at. %Co-22 at. %Cr-12 at. %Pt arenot formed, and the thickness of magnetic layers 14 and 14′ of the 63at. %Co-21 at. %Cr-12 at. %Pt-4 at. %B is set to 18 nm. Experiments areconducted by changing the molybdenum concentration in a range from 10at. % to 40 at. % in the Cr—Mo alloy underlayers. As a result, the valueof Hc takes a maximum value for 80 at. %Cr-20 at. %Mo, which is henceemployed in comparison example 6.

TABLE 4 Thickness of Thickness of 66at%Co- 63at%Co-21at%Cr-22at%Cr-12at%Pt 12at%Pt-4at%B intermediate Br × t Hc S/N Resolutionmagnetic layer (nm) magnetic layer (nm) (T · nm) (kA/m) S* (dB) (%)Embodiment 5a 9 9 6.3 302 0.70 20.4 58.3 Embodiment 5b 12 6 5.8 311 0.6720.6 57.8 Embodiment 5c 6 12 5.6 298 0.68 20.5 58.3 Comparative None 185.7 265 0.65 19.8 55.8 Example 4 Comparative 21 None 1.4 53 0.22 — —Example 5

TABLE 5 Thickness of 63at%Co-21at%Cr- Thickness of 12at%Pt-4at%B80at%Cr-20at%Mo Br × t Hc S/N Resolution magnetic layer (nm) secondunderlayer (nm) (T · nm) (kA/m) S* (dB) (%) Comparative 21 15 5.2 2520.58 19.1 55.6 Example 6

Table 4 shows magnetic properties and read/write characteristics of themedium of the fifth embodiment and the fourth comparison example andTable 5 shows those of the medium of the fifth and sixth comparisonexamples. As the magnetic properties, coercivity Hc, coercivitysquareness S*, and product Br×t between total thickness t of themagnetic layers and the intermediate magnetic layers and residualmagnetic flux density Br are measured by a vibrating sample magnetometerat a room temperature with a maximum magnetic field intensity of 800kA/m (10 kilooersted). The read/write characteristics are measured by amagnetic head including a read-out element of spin valve type having ashield gap length Gs of 0.15 micrometers and an inductive write elementhaving a gap length of 0.2 micrometer. In the tables, S indicates a readoutput for 8660 fr/mm (220 kFCI) and N is a medium noise at a linearrecording density of 17300 fr/mm (440 kFCI), and S/N (ratio) is used forevaluation. To evaluate a recording resolution, there is employed“Resolution” which is a ratio of the read output at 17300 fr/mm (440kFCI) to that at 8660 fr/mm (220 kFCI). The recording density of themedium increases as S if/N and Resolution become greater. For mediumsamples a to c of the fifth embodiment, coercivity Hc can be adjusted byratios respectively of the Co—Cr—Pt—B magnetic layers and the Co—Cr—Ptintermediate magnetic layers as can be seen from Table 4. Medium a to chas higher values of S if/N and Resolution than the fourth to sixthcomparison examples.

Embodiment 6

As embodiment 6, a magnetic recording medium is produced in the layerconfiguration of the fifth embodiment. The medium includes a substrate10 of a chemically tempered alumino-silicate of 2.5 inch type. Substrate10 is first washed and a plurality of layers are fabricated thereon witha tact of eight seconds by a sputtering apparatus (MDP250B) of Intevac.On substrate 10, there are fabricated 25 nm thick seed films 11 and 11′with a 60 at. %Co-30 at. %Cr-10 at. %Zr alloy, 25 nm thick underlayers12 and 12′ with an 78 at. %Cr-22 at. %Ti alloy, 8 nm thick magneticintermediate layers 13 and 13′ with a 67 at. %Co-21 at. %Cr-12 at. %Ptalloy, 8 nm thick magnetic layers 14 and 14′ with a 63 at. %Co-20 at.%Cr-12 at. %Pt-5 at. %B alloy, and 5 nm thick protective carbon layers15 and 15′. In each film fabrication, an argon gas has a pressure of0.87 Pa (7.5 mTorr). An oxygen partial pressure monitored by mainchamber 29 during the film fabrication is from about 1×10⁻⁷ Pa (8×10⁻¹⁰Torr) to about 7×10⁻⁷ Pa (5×10⁻⁹ Torr). The seed layers are manufacturedin seed film chamber 22 without heating the substrate and are thenheated up to 230□ by a lamp heater in heating chamber 23. The seedlayers are thereafter exposed to an atmosphere of a mixed gas of 95 vol%Ar-4 vol %N2-1 vol %O₂ at 0.9 Pa (7 mTorr) at a gas flow rate of 21sccm for 3.5 seconds in oxidization chamber 24. Thereafter, therespective films are fabricated thereon in underlayer chamber 25,magnetic intermediate film chamber 26, magnetic film chamber 27, andprotective film chambers 28 and 28′. After the protective carbon layersare manufactured, a lubricant containing perfluoroalkyl-polyether as itsprimary element is applied thereon to form 1.5 nm thick lubricant films16 and 16′.

TABLE 6 Thickness of Thickness of 67at%Co- 63at%Co-20at%Cr-21at%Cr-12at%Pt 12at%Pt-5at%B intermediate Br × t Hc S/N Resolutionmagnetic layer (nm) magnetic layer (nm) (T · nm) (kA/m) S* (dB) (%)Embodiment 6 8 8 5.6 322 0.71 20.5 59.1

As a result, the thicknesses of the magnetic films and the intermediatemagnetic films can be reduced when compared with those of the fifthembodiment; moreover the value of Hc is increased. Consequently, theread/write characteristics of the sixth embodiment are equal to or morethan those of the fifth embodiment as shown in Table 6.

The recording medium above is actually installed in a magnetic recordingdisk apparatus to evaluate read/write characteristics of the mediumusing a giant magnetoresistive (GMR) head under the conditions of a 24nm magnetic spacing between the head and the magnetic film surface, alinear recording density of 510 kBPI, and a track density of 41 kTPI. Asa result, the medium of the fifth and that of the sixth embodimentssatisfactorily satisfy the specifications of read/write characteristicsfor a magnetic reading disk apparatus with a surface recording densityof 21 gigabits per square inch. Even after the medium is allowed tostand at 70□ for 100 hours, the bit error rate is deteriorated only by0.5 order of magnitude. In accordance with the present invention, thesubstrate and the glass substrate are not particularly restricted.Namely, the advantages above can be attained by any known substrates formagnetic recording medium such as an aluminum alloy substrate plated bya Ni—P alloy, glass ceramics, and a silicon substrate.

Next, description will be given of an embodiment in which theintermediate layers of FIG. 1 are fabricated with a nonmagneticsubstance.

Embodiment 7

A magnetic recording medium is fabricated as embodiment 7 in the samelayer configuration and under the same condition as for the fifthembodiment only excepting that each of intermediate layers 13 and 13′ ofFIG. 1 showing the layer configuration is replaced with a 7 nm thick 58at. %Co-30 at. %Cr-12 at. %Pt alloy layer and each of magnetic layers 14and 14′ is replaced with a 18 nm thick 62 at. %Co-21 at. %Cr-12 at.%Pt-5 at. %B alloy layer. Magnetic properties of the medium of theseventh embodiment are evaluated by the vibrating sample magnetometer.Resultantly, coercivity is 330 kA/m (4.15 kilooersted), coercivitysquareness is 0.69, Br×t is 5.4 T.nm (54 Gauss.micron). That is, highcoercivity is obtained with low Br×t. Moreover, a magnetic recordingmedium is fabricated in the same layer configuration and under the samecondition as for the seventh embodiment only excepting that 30 nm thickintermediate layers 13 and 13′ are manufactured with 58 at. %Co-30 at.%Cr-12 at. %Pt alloy and magnetic layers 14 and 14′ are not fabricated.Read/write characteristics of this medium are evaluated by a vibratingsample magnetometer (BHV-50 of Riken-Denshi). Resultantly, themagnetization measuring range is 3.1×10⁻¹² Wb-m (0.0025 emu) and thevalue of Br×t is too small for the measurement, and intermediate layers13 and 13′ of 58 at. %Co-30 at. %Cr-12 at. %Pt become substantiallynonmagnetic. The medium of the seventh embodiment has read/writecharacteristics satisfying the specifications of a magnetic recordingdisk apparatus with a surface recording density of 30 gigabits persquare inch. Even after the medium is allowed to stand at 70□ for 100hours, the bit error rate is deteriorated only by 0.5 order of magnitudeor less. When the surface recording density is 30 gigabits per squareinch or more, it is effective to fabricate substantially nonmagneticintermediate Co—Cr—Pt layers as in this embodiment. The intermediatelayers favorably have composition including a chromium concentration offrom 28 at. % to 40 at. % and a platinum concentration of from 8 at. %to 20 at. %. Thanks to the composition, the intermediate layersdesirably become substantially nonmagnetic and the C—Cr—Pt—Ta layersfavorably grow epitaxially.

Embodiment 8

A magnetic recording medium is fabricated as embodiment 8 in accordancewith the medium of the sixth embodiment by replacing magnetic layers 14and 14′ with 8 nm thick 63 at. %Co-20 at. %Cr-12 at. %Pt-1 at. %Ta-4 at.%B alloy layers. Table 7 shows magnetic properties and read/writecharacteristics of the medium evaluated in the same way as for the fifthembodiment. As can be seen from Table 7, the value of S/N ratio isincreased, as compared with the medium of the sixth embodiment, by usingthe magnetic films of an alloy to which tantalum and boron aresimultaneously added.

TABLE 7 Thickness of 63at%Co-20at%Cr- Thickness of 67at%Co-12at%Pt-1at%Ta- 21at%Cr-12at%Pt 4at%B magnetic intermediate Br × t HcS/N Resolution layer (nm) magnetic layer (nm) (T · nm) (kA/m) S* (dB)(%) Embodiment 8 8 8 5.3 308 0.70 21.1 58.1

The magnetic recording medium above is actually installed in a magneticrecording disk apparatus to evaluate read/write characteristics of themedium using a giant magnetoresistive (GMR) head under the conditions ofa 23 nm magnetic spacing between the head and the magnetic film surface,a linear recording density of 535 kBPI, and a track density of 43 kTPI.As a result, the medium of the eighth embodiment satisfactorilysatisfies the specifications of read/write characteristics for amagnetic reading disk apparatus with a surface recording density of 23gigabits per square inch. Even after the medium is allowed to stand at70□ for 100 hours, the bit error rate is deteriorated only by 0.5 orderof magnitude.

Embodiment 9

FIG. 9 shows a layer configuration of embodiment 9 of a magneticrecording medium. This medium is produced by additionally fabricatingsecond underlayers 17 and 17′ respectively between underlayers 12 and12′ and intermediate layers 13 and 13′ of the layer configuration shownin FIG. 1. A sputtering apparatus (MDP250B) of Intevac is employed tomanufacture a plurality of layers like in the fifth embodiment. Themedium includes a substrate 10 of a chemically tempered alumino-silicateof 2.5 inch type. Substrate 10 is first washed. On substrate 10, thereare fabricated 40 nm thick seed films 11 and 11′ with a 65 at. %Ni-20at. %Cr-15 at. %Zr alloy, 15 nm thick underlayers 12 and 12′ with a 80at. %Cr-20 at. %Ti alloy, 7 nm thick second underlayers 17 and 17′ witha chromium alloy, magnetic intermediate layers 13 and 13′ with a 65 at.%Co-21 at. %Cr-14 at. %Pt alloy, magnetic layers 14 and 14′ with a 62at. %Co-20 at. %Cr-14 at. %Pt-4 at. %B alloy, and 5 nm thick protectivecarbon layers 15 and 15′. In each film fabrication, an argon gas has apressure of 0.9 Pa (7 mTorr) as in the fifth embodiment. The seed layersare manufactured without heating the substrate and are then heated up to220□by a lamp heater. The seed layers are thereafter exposed to anatmosphere of a mixed gas of 99 vol %Ar-1 vol %N₂-1 vol %O₂ at 0.9 Pa (7mTorr) at a gas flow rate of 20 sccm for 3.5 seconds. Thereafter, therespective films are fabricated thereon. After the protective carbonlayers are manufactured, a lubricant containing perfluoroalkyl-polyetheras its primary element is applied thereon to form 1.5 nm thick lubricantfilms 16 and 16′. Samples a and b are produced with the secondunderlayers respectively of a 75 at. %Cr-25 at. %Mo alloy and a 75 at.%Cr-25 at. %W alloy as shown in Table 8. Table 8 also shows magneticproperties and read/write characteristics of the medium evaluated in thesame way as for the fifth embodiment. As can be seen from this table,the magnetic recording medium of the ninth embodiment respectivelyincluding the second underlayers respectively of a 75 at. %Cr-25 at. %Moalloy and a 75 at. %Cr-25 at. %W alloy has higher values of Resolutionwhen compared with the medium of the sixth embodiment.

TABLE 8 Composition of second Br × t Hc S/N Resolution underlayer (T ·nm) (kA/m) S* (dB) (%) Em- 75at%Cr- 5.1 343 0.71 21.8 61.2 bodi- 25at%Moment 9a Em- 75at%Cr- 4.9 329 0.69 21.1 60.1 bodi- 25at%W ment 9b

The magnetic recording medium above is actually installed in a magneticrecording disk apparatus to evaluate read/write characteristics of themedium using a giant magnetoresistive (GMR) head under the conditions ofa 23 nm magnetic spacing between the head and the magnetic film surface,a linear recording density of 560 kBPI, and a track density of 43 kTPI.As a result, the medium of the ninth embodiment satisfactorily satisfiesthe specifications of read/write characteristics for a magnetic readingdisk apparatus with a surface recording density of 24 gigabits persquare inch. Even after the medium is allowed to stand at 70□ for 100hours, the bit error rate is deteriorated only by 0.5 order ofmagnitude.

The magnetic recording medium of the present invention advantageouslyreduces the medium noise and is resistive against thermal fluctuation.Thanks to the magnetic recording medium and the magnetoresistive head ofthe present invention, there can be implemented a magnetic recordingapparatus having a recording density of five gigabits per square inch ormore.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

What is claimed is:
 1. A magnetic recording medium, comprising: anunderlayer including a nonmagnetic alloy containing chromium andtitanium; an intermediate layer of an alloy consisting of Co—Cr—Pt; anda magnetic layer of an alloy consisting essentially of Co—Cr—Pt—Ta andat least one element selected from a group consisting of niobium, boron,and titanium on the intermediate layer.
 2. A magnetic recording mediumin accordance with claim 1, wherein the magnetic layer has a compositionof said at least one element concentration ranging from 1 at. % to 3 at.%.
 3. A magnetic recording medium in accordance with claim 1, whereinthe intermediate layer has a composition of a chromium concentrationranging from 18 at. % to 24 at. % platinum concentration ranging from 8at. % to 20 at. %.
 4. A magnetic recording medium comprising, anunderlayer including a nonmagnetic alloy containing chromium andtitanium; a magnetic layer including a Co—Cr—Pt—Ta alloy in which theconcentration of tantalum is increased consecutively toward the mediumsurface, and a bottom side of the magnetic layer has an alloy consistingessentially of Co—Cr—Pt.
 5. A magnetic recording medium comprising: anunderlayer including a nonmagnetic alloy containing chromium andtitanium; a magnetic layer including a Co—Cr—Pt—B alloy in which theconcentration of boron is increased consecutively toward the mediumsurface, and a bottom side of the magnetic layer has an alloy consistingessentially of Co—Cr—Pt.